1. Often Disparaging and Offensive. a resident of one country who was born in or owes allegiance to another country and has not acquired citizenship by naturalization in the country of residence (distinguished from citizen). See also resident alien, illegal alien.
  2. a foreigner.
  3. a person who has been estranged or excluded.
  4. a creature from outer space; extraterrestrial(def 2).


  1. residing under a government or in a country other than that of one’s birth without having or obtaining the status of citizenship there.
  2. belonging or relating to aliens: alien property.
  3. unlike one’s own; strange; not belonging to one: alien speech.
  4. adverse; hostile; opposed (usually followed by to or from): ideas alien to modern thinking.
  5. extraterrestrial(def 1).


  1. a person owing allegiance to a country other than that in which he lives; foreigner
  2. any being or thing foreign to the environment in which it now exists
  3. (in science fiction) a being from another world, sometimes specifically an extraterrestrial


  1. unnaturalized; foreign
  2. having foreign allegiancealien territory
  3. unfamiliar; strangean alien quality in a work of art
  4. (postpositive and foll by to) repugnant or opposed (to)war is alien to his philosophy
  5. (in science fiction) of or from another world


  1. (tr) rare to transfer (property, etc) to another

mid-14c., “strange, foreign,” from Old French alien “alien, strange, foreign; an alien, stranger, foreigner,” from Latin alienus “of or belonging to another, foreign, alien, strange,” also, as a noun, “a stranger, foreigner,” adjectival form of alius “(an)other” (see alias). Meaning “not of the Earth” first recorded 1920. An alien priory (c.1500) is one owing obedience to a mother abbey in a foreign country.


“foreigner, citizen of a foreign land,” from alien (adj.). In the science fiction sense, from 1953.

  1. Introduced to a region deliberately or accidentally by humans. Starlings, German cockroaches, and dandelions are species that are alien to North America but have become widely naturalized in the continent. Compare endemic indigenous.
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